An inorganic / organic double-layer composite-coated metal magnetic powder core and its preparation method

Abstract

The present invention discloses an inorganic / organic double-layer composite coated metal magnetic powder core and a preparation method thereof. The preparation method comprises the following steps: (1) adding an iron-based soft magnetic material to a phosphoric acid solution, reacting, washing, adding a polyamic acid solution, reacting again, and drying to obtain an inorganic / organic double-layer composite coated iron-based soft magnetic material; (2) pressing the organic / organic double-layer composite coated iron-based soft magnetic material into a ring-shaped green body, annealing and heat treating, to obtain an inorganic / organic double-layer composite coated metal magnetic powder core. The present invention uses an inorganic / organic double-layer composite coating technology to make the coating layer uniform and dense, with high resistivity and good interface bonding, thereby achieving the effects of improving the magnetic permeability of the metal magnetic powder core, improving the frequency stability of the magnetic permeability, and reducing losses.

Description

Technical Field

[0001] The present invention relates to the technical field of soft magnetic functional materials, and in particular to an inorganic / organic double-layer composite-coated metal magnetic powder core and a preparation method thereof. Background Art

[0002] Soft Magnetic Composite (SMC) cores, composed of surface-insulated metal powder particles and manufactured using powder metallurgy techniques, can be pressed into complex shapes in a single step, exhibiting excellent isotropic magnetic properties. Compared to silicon steel sheets, SMC offers numerous advantages, including magnetic isotropy, the ability to accommodate complex shapes, low eddy current losses, and low cost. SMC has the potential to replace silicon steel sheets in certain applications for motor stator cores. In recent decades, with the development of SMC materials, international researchers have conducted extensive research on SMC applications in motors, achieving success in many commercial applications. However, SMC materials for motors still have significant drawbacks, such as low magnetic permeability and poor saturation characteristics. Furthermore, the trend toward higher frequencies and higher speeds in motors places higher demands on their loss control.

[0003] How to fully leverage the advantages of SMC and mitigate its shortcomings has become a hot topic and a challenge in research on this material. The insulation coating is the most critical step, playing a decisive role in improving the resistivity of magnetic powder cores and reducing high-frequency losses. Furthermore, the properties and amount of the insulating material directly affect the compacting effect, and thus the magnetic permeability of the SMC. Currently, the insulation coating of SMC materials for motors is primarily based on organic polymers and inorganic oxides. In recent years, a range of SMC products and insulation coating processes have been rapidly developed both domestically and internationally to address different application areas. The use of organic polymers as insulation coating materials has become commercially available. In 2005, JFE Corporation of Japan developed and began production of an iron-resin mixed powder. This SMC material is based on pure iron-based reduced iron powder with a particle size of approximately 100μm. Sumitomo Electric Industries, Ltd. of Japan has developed a new resin-bonded SMC material, "FM-CM." While adding a small amount of resin, it achieves high compact density, excellent high-frequency magnetic properties, and high heat resistance. While an organic resin coating can impart high resistivity to the compact and reduce eddy current losses, its overall performance is insufficient to replace traditional silicon steel sheets in core materials. Due to the large amount of insulating resin incorporated, the magnetic particle content per unit volume is reduced, resulting in a low DC magnetic flux density. Furthermore, the properties of the resin limit the heat treatment temperature of the compact. Due to the poor heat resistance of the insulating coating, the mechanical strength of the material at 200°C is significantly reduced. To address the low heat resistance of organic polymers, researchers have successfully developed a technique for directly coating the surface of magnetic powder with an insulating film. This double-layer coating method for iron powder particles involves first applying an extremely thin phosphate coating 10-100 μm thick to the iron powder surface. Then, only a minimal amount of resin is added to achieve the insulating resin coating during the pressing and heat treatment process, ultimately resulting in a soft magnetic material with high insulation and magnetic properties. This technique not only increases the compact density and enhances the thermal stability of the insulating coating, but also demonstrates that the phosphate coating inhibits oxidation of the iron powder surface. The commercial phosphate insulation coating technology invented by Swedish Hoganas represents the international advanced level, effectively reducing eddy current loss and having good magnetic and mechanical properties. However, since the raw materials still contain organic components, the heat treatment temperature is still limited. Somaloy produced by Swedish Hoganas TM The maximum recommended heat treatment temperature for 500°C is around 500°C; otherwise, insulation properties will deteriorate dramatically. To further increase the heat treatment temperature, inorganic oxides as insulating coating materials have become a current research focus. European research heat sources use a sol-gel process to coat the surface of iron powder with a silicon oxide layer. However, thin coatings have poor wettability for the iron powder, while overly thick coatings reduce the density of the SMC material and deteriorate its magnetic properties. Summary of the Invention

[0004] The primary purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art and to provide a metal magnetic powder core with an inorganic / organic double-layer composite coating.

[0005] Another object of the present invention is to provide a method for preparing the above-mentioned inorganic / organic double-layer composite-coated metal magnetic powder core.

[0006] The object of the present invention is achieved by the following technical solution: A method for preparing an inorganic / organic double-layer composite-coated metal magnetic powder core comprises the following steps:

[0007] (1) Preparation of inorganic / organic double-layer composite coated iron-based soft magnetic powder

[0008] The iron-based soft magnetic material and the phosphoric acid solution are mixed, reacted, washed, and a polyamic acid solution is added, reacted again, and dried to obtain an inorganic / organic double-layer composite coated iron-based soft magnetic material;

[0009] (2) Preparation of metal magnetic powder core coated with inorganic / organic double layer composite

[0010] The organic / organic double-layer composite coated iron-based soft magnetic material in step (1) is pressed into a ring-shaped green body, and subjected to annealing heat treatment to obtain an inorganic / organic double-layer composite coated metal magnetic powder core.

[0011] The iron-based soft magnetic material in step (1) is preferably at least one of pure iron, iron-silicon alloy, iron-silicon-aluminum alloy, iron-nickel alloy, iron-nickel-molybdenum alloy, iron-based amorphous alloy, and iron-based nanocrystalline alloy.

[0012] The iron-based soft magnetic powder in step (1) is preferably a powder of 100-150 mesh.

[0013] The amount of the phosphoric acid solution in step (1) is preferably calculated based on a ratio of 0.5-2% of phosphoric acid to the mass of the iron-based soft magnetic material.

[0014] The concentration of the phosphoric acid solution in step (1) is preferably 0.7% to 2.7% by volume.

[0015] The solvent of the phosphoric acid solution in step (1) is preferably ethanol.

[0016] The reaction time in step (1) is preferably 0.5-2 h.

[0017] The washing in step (1) is preferably performed by washing with anhydrous ethanol.

[0018] The amount of the polyamic acid solution in step (1) is preferably calculated based on a ratio of 0.5-2% of the polyamic acid to the mass of the iron-based soft magnetic material.

[0019] The concentration of the polyamic acid solution in step (1) is preferably 0.5% to 3% by volume.

[0020] The solvent of the polyamic acid solution in step (1) is preferably dimethylacetamide.

[0021] The time for the second reaction in step (1) is preferably 15-30 min.

[0022] The reaction and the subsequent reaction in step (1) are preferably stirred reactions.

[0023] The drying in step (1) is preferably carried out at 150-180° C. for 1-3 hours.

[0024] The pressing conditions in step (2) are preferably: molding pressure 1000-2000 MPa, holding time 5-10 s.

[0025] The annealing heat treatment in step (2) is preferably annealing heat treatment at 200-500° C. for 1-3 hours.

[0026] The annealing heat treatment in step (2) is preferably performed under vacuum or inert atmosphere.

[0027] The inert atmosphere is preferably argon or nitrogen.

[0028] An inorganic / organic double-layer composite-coated metal magnetic powder core is prepared by the above-mentioned preparation method.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The present invention utilizes an inorganic / organic dual-layer composite coating technology to achieve a uniform, dense coating with high resistivity and excellent interfacial bonding. The outer organic layer improves the frequency stability of the magnetic permeability and protects the inner phosphate layer. The inner phosphate layer effectively coats the metal powder surface, imparting complete insulation properties to the metal magnetic powder core. This improves the magnetic permeability of the metal magnetic powder core, improves its frequency stability, and reduces losses. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a comparison chart of the magnetic permeabilities of metal powder cores coated with single-layer phosphoric acid, single-layer polyamic acid, and double-layer phosphoric acid / polyamic acid.

[0032] Figure 2 This is a comparison chart of the magnetic loss of metal magnetic powder cores coated with single-layer phosphoric acid, single-layer polyamic acid, and double-layer phosphoric acid / polyamic acid. DETAILED DESCRIPTION

[0033] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0034] Example 1

[0035] (1) Preparation of inorganic / organic double-layer composite coated iron-based soft magnetic powder

[0036] First, 150-mesh pure iron powder was sieved. 1 mL of phosphoric acid (0.6% of the pure iron powder's mass fraction) was weighed, and 50 mL of anhydrous ethanol solution was added to the phosphoric acid as a solvent to obtain a phosphoric acid solution. The pure iron powder was added to the phosphoric acid solution and stirred for 30 minutes. The powder was then washed with a small amount of anhydrous ethanol. A polyamic acid solution containing 1% of the pure iron powder's mass fraction (1 mL of polyamic acid was added to 50 mL of dimethylacetamide as a solvent) was added and stirred thoroughly for 15 minutes. Finally, the solution was dried in a drying oven at 180°C for 1 hour to obtain an inorganic / organic double-layer composite coated iron-based soft magnetic powder.

[0037] (2) Preparation of metal magnetic powder core coated with inorganic / organic double layer composite

[0038] The resulting inorganic / organic dual-layer composite-coated iron-based soft magnetic powder was then pressed into a ring-shaped green compact at a molding pressure of 1500 MPa and a holding time of 5 seconds. This green compact was then annealed in a tubular furnace at 500°C under vacuum for 1 hour to obtain a metal magnetic powder core with an inorganic / organic dual-layer composite coating.

[0039] Example 2-3, Comparative Example 1-2

[0040] The methods for preparing the metal magnetic powder cores in Examples 2-3 and Comparative Examples 1-2 were the same as in Example 1, with the differences shown in Table 1. The magnetic loss and permeability of the metal magnetic powder cores in Examples 1-3 and Comparative Examples 1-2 were measured at 1 T / 1000 Hz. Specific testing methods: Magnetic properties of the samples were tested using an IWATSU BH analyzer (SY-8219) in accordance with standard SJ20966-2006. The testing conditions were: room temperature 25°C, an applied magnetic field of 1 T, and a frequency of 200-1000 Hz.

[0041] Table 1

[0042]

[0043] As can be seen from Table 1, the magnetic loss of the metal magnetic powder cores coated with a single layer of phosphoric acid and a single layer of polyamic acid is significantly higher than that of Examples 1-3 coated with a double layer of phosphoric acid / polyamic acid. The magnetic permeability of the metal magnetic powder cores coated with a single layer of phosphoric acid and a single layer of polyamic acid is lower than that of Examples 1-3 coated with a double layer of phosphoric acid / polyamic acid.

[0044] Figure 1 and 2 The following chart compares the magnetic loss and permeability of metal magnetic powder cores coated with a single layer of phosphoric acid (Comparative Example 1), a single layer of polyamic acid (Comparative Example 2), and a double layer of phosphoric acid / polyamic acid (Example 1) at different frequencies. It is clear that the metal magnetic powder core coated with a double layer of phosphoric acid / polyamic acid (Example 1) exhibits excellent permeability stability and low magnetic loss at different frequencies.

[0045] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A method for preparing an inorganic / organic double-layer composite-coated metal magnetic powder core, characterized in that: The following steps are involved: (1) Preparation of inorganic / organic double-layer composite coated iron-based soft magnetic powder The iron-based soft magnetic material and the phosphoric acid solution are mixed, reacted, washed, and a polyamic acid solution is added, reacted again, and dried to obtain an inorganic / organic double-layer composite coated iron-based soft magnetic material; (2) Preparation of metal magnetic powder core coated with inorganic / organic double layer composite The inorganic / organic double-layer composite coated iron-based soft magnetic material in step (1) is pressed into a ring-shaped green body, and subjected to annealing heat treatment to obtain an inorganic / organic double-layer composite coated metal magnetic powder core; The amount of the phosphoric acid solution in step (1) is calculated based on a ratio of 0.8% of phosphoric acid to the mass of the iron-based soft magnetic material; the concentration of the phosphoric acid solution is 0.7%-2.7% by volume; The amount of the polyamic acid solution in step (1) is calculated based on the ratio of polyamic acid to the mass of the iron-based soft magnetic material; the concentration of the polyamic acid solution is 0.5%-3% by volume; The reaction time in step (1) is 0.5 h; the second reaction time is 15 min; the drying is performed at 180° C. for 1 h; The pressing conditions in step (2) are: molding pressure 1500 MPa, holding time 5 s; The annealing heat treatment in step (2) is annealing heat treatment at 500° C. for 1 hour, and the annealing heat treatment is performed under vacuum or inert atmosphere.

2. The method for preparing the inorganic / organic double-layer composite-coated metal magnetic powder core according to claim 1, characterized in that: The iron-based soft magnetic material in step (1) is at least one of pure iron, iron-silicon alloy, iron-silicon-aluminum alloy, iron-nickel alloy, iron-nickel-molybdenum alloy, iron-based amorphous alloy, and iron-based nanocrystalline alloy; The iron-based soft magnetic material in step (1) is a powder of 100-150 mesh.

3. The method for preparing the inorganic / organic double-layer composite-coated metal magnetic powder core according to claim 1 or 2, characterized in that: The solvent of the phosphoric acid solution in step (1) is ethanol; The solvent of the polyamic acid solution in step (1) is dimethylacetamide.

4. The method for preparing the inorganic / organic double-layer composite-coated metal magnetic powder core according to claim 1, characterized in that: The washing in step (1) is washing with anhydrous ethanol; The reaction and the re-reaction in step (1) are stirring reactions.

5. The method for preparing the inorganic / organic double-layer composite-coated metal magnetic powder core according to claim 1, characterized in that: The inert atmosphere is argon or nitrogen.

6. An inorganic / organic double-layer composite coated metal magnetic powder core, characterized in that: It is prepared by the preparation method according to any one of claims 1 to 5.

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